1. Field of the Invention
The present invention relates to a lens driving apparatus, used in an optical system of an optical device such as a camera.
2. Related Background Art
Conventionally known as a lens barrel, used in an optical system of an optical device such as a camera, for changing its power and adjusting its focus is one having four lens groups, all of which are attached to a frame expandable from the camera body, whereas the lens groups are appropriately moved in the optical axis direction by use of a cam mechanism so as to change the power and adjust the focus, as disclosed in Japanese Patent Application Laid-Open No. HEI 7-20369.
This lens barrel comprises a barrier blade, disposed in front of a taking optical system, for opening/closing an optical path; a lens driving mechanism for advancing/retracting a part of the taking optical system upon a focusing operation of the taking optical system; a barrier driving mechanism for opening/closing the barrier blade; a first transmission mechanism for transmitting a driving force of a driving source to the lens driving mechanism; and a second transmission mechanism for transmitting the driving force of the driving source to the barrier driving mechanism, in which the transmission of the driving force to the second transmission mechanism is switched via a clutch mechanism as appropriate. The switching of the clutch mechanism is carried out by utilizing a pivotal member, so as to enhance the space efficiency, thereby reducing the size of the camera.
In order to realize precise focus adjustment in such a lens barrel, however, it is preferred that the position of a moving lens group be detected directly so as to move this lens group accurately.
While a position detecting sensor is necessary for detecting the position of a lens group, the position detecting sensor becomes greater in order to detect the position of the lens group in the whole moving area of the lens group, whereby the cost of parts may rise.
In view of such a technical problem, it is an object of the present invention to provide a lens driving apparatus which can prevent the lens barrel from increasing its size and cost while making it possible to correctly detect positions of movable lens groups by use of a simple position detecting sensor.
In order to achieve such an object, the present invention provides a lens driving apparatus comprising a lens optical system in which a plurality of lens groups are disposed along an optical axis, at least one of the lens groups being a movable lens group; a lens moving mechanism for moving the movable lens group by transmitting a moving force of a driving source thereto; detecting means for detecting the movable lens group passing a reference position; and drive control means for driving and controlling the driving source so as to move the movable lens group at two or more speeds different from each other; wherein, when the movable lens group passes the reference position, the drive control means moves the movable lens group at a speed which is not the highest in the different speeds.
The lens driving apparatus in accordance with the present invention may be configured such that, after the movable lens group passes the reference position, the drive control means moves the movable lens group at the highest speed in the different speeds and then slows down the moving speed of the movable lens group stepwise as the movable lens group approaches a stop position.
In the lens driving apparatus in accordance with the present invention, the movement of the movable lens group is a movement for focus adjustment in the lens optical system.
According to these aspects of the present invention, the moving speed of the movable lens group is not the highest speed when it passes the reference position, whereby the passage of the movable lens group at the reference position can be detected accurately. As a consequence, focusing can accurately be carried out by moving the movable lens group.
Also, the present invention provides a lens driving apparatus comprising a lens optical system in which a plurality of lens groups are disposed along an optical axis, at least one of the lens groups being a movable lens group; a lens moving mechanism for moving the movable lens group by transmitting a moving force of a driving source thereto; detecting means for detecting the movable lens group passing a reference position set within a moving area of the movable lens group; and drive control means for driving and controlling the driving source so as to move the movable lens group at two or more speeds different from each other; wherein, after the movable lens group moves toward an end portion within the moving area and passes the reference position, the drive control means slows down the moving speed of the movable lens group.
According to this aspect of the present invention, the moving speed of the movable lens group is slowed down after it passes the reference position. Therefore, the movable lens group can be prevented from colliding with a stopper installed at an end portion of the moving area due to an impetus of the movement, and gears of the lens moving mechanism can be kept from meshing with each other upon the collision and thus failing to rotate in reverse, which may become a severe failure, for example.
Further, the present invention provides a lens driving apparatus comprising a lens optical system in which a plurality of lens groups are disposed along an optical axis, at least one of the lens groups being a movable lens group; a lens moving mechanism for moving the movable lens group by transmitting a moving force of a driving source thereto; movement control means for driving and controlling the driving source so as to move the movable lens group from a wait position to a predetermined stop position; and detecting means for detecting the movable lens group passing a reference position set between the wait and stop positions by reversing an output; wherein, when the output of the detecting means is reversed upon movement of the movable lens group, the movement control means moves the movable lens group toward the stop position by a predetermined distance and then continues to move the movable lens group when the output of the detecting means is not reversed.
According to this aspect of the present invention, even when chattering occurs upon movement of the movable lens group, whereby the output of the detecting means is reversed, the movement of the movable lens group continues. Therefore, even when chattering is generated, the movable lens group can securely be moved to a predetermined stop position without mistaking the reference position.
Also, the present invention provides a lens driving apparatus comprising a lens optical system in which a plurality of lens groups are disposed along an optical axis, at least one of the lens groups being a movable lens group; a lens moving mechanism for moving the movable lens group by transmitting a moving force of a driving source thereto; detecting means for detecting a position of the movable lens group; and drive control means for driving and controlling the driving source so as to move the movable lens group at two or more speeds different from each other; wherein, when the drive control means is loaded with a battery for supplying power thereto, the drive control means moves the movable lens group at a speed which is not the highest in the different speeds, and the detecting means detects a position of the movable lens group upon the movement.
According to this aspect of the present invention, when the drive control means is loaded with a battery for supplying power thereto, the movable lens group is moved at a speed which is not the highest, and the position of the movable lens group is detected upon this movement. As a consequence, the position of the movable lens group can be detected accurately. Since the position is detected accurately, accuracy can be improved in the focusing upon movement of the movable lens thereafter.
The lens driving apparatus in accordance with the present invention may further comprise a first driving transmission mechanism for transmitting the driving force of the driving source to a barrier opening/closing mechanism; and a second driving transmission mechanism for transmitting the driving force of the driving source to the lens moving mechanism, wherein the movement of the movable lens group and opening/closing of a barrier in the lens optical system are adapted to synchronize with each other upon driving the driving source.
According to this aspect of the present invention, the movement of the movable lens group and the opening/closing of the barrier in the lens optical system synchronize with each other upon driving the driving source, whereby the barrier opening/closing state can indirectly be detected when the position of the movable lens group is detected. Therefore, sensors for detecting the barrier opening/closing, and the like can be omitted.